The first of possibly hundreds of explosives buried at Tipton Army Airfield were detonated this week as workers began a tedious, painstaking cleanup of the area that is expected to take at least six months and make the site safe for civilian operation.

The workers, employees of Human Factors Applications Inc., started digging Wednesday and found several fuses and an unexploded hand grenade.

They blew up those devices with a small cylinder-shaped explosive, said Richard Johnson, project manager for Human Factors.

The Army hired the Waldorf company to conduct the $2.5 million cleanup of 310 acres at the airfield.

A team of 33 ordnance removal specialists will work its way around the airfield in 100-by-100-foot grids.

The specialists will carefully sweep the earth with magnetometers that can detect pieces of metal as small as nails, Mr. Johnson said.

Yesterday, hundreds of knee-high yellow flags indicating where metal had been found covered part of a hillside at eastern end of the airfield. All ordnance dug up is exploded between 3:30 p.m. and 5 p.m. the day it is found, Mr. Johnson said.

Sandbags are placed over the material to muffle the sound, he said.

"The noise is going to cause very little disruption to people" in the area, Mr. Johnson said.

The cleanup has been delayed almost six months because of delays in planning and federal funding.

Anne Arundel and Howard counties wanted to open Tipton as a civilian airport for noncommercial flights in October. Anne Arundel officials want no more delays.

"The greatest impediment for us taking over that airfield is the cleanup," said Sam Minnitte, project manager of the airfield for Anne Arundel County.

The airfield is the last of more than 8,000 acres of Fort Meade property to be converted to civilian use under the Base Closure and Realignment Act of 1988.

The cleanup will clear ordnance to a depth of 4 feet, except

under roads, runways, buildings and three landfills at the airport.

Workers will be particularly careful to avoid digging in the landfills, because the sites may contain ordnance and hazardous chemicals, said Sara Gracey, an environmental coordinator at Fort Meade.

The landfills, which haven't been used for at least 30 years, probably will be sealed to prevent leaching, she said.

Ordnance buried at the former training area could date back to World War I, officials said.

Mr. Johnson said he expects to uncover an assortment of rockets and grenades.

"It's not something you would see at an arms convention," he said. "It has been laying around for a while."